# pitch-expansion-series

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Sorry for the newbie query.  Can anyone give me a clear explanation of what the arguments in 'pitch-expansion-series' actually do?

Thanks.

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pitch-expansion-series size interval count pitch

&key max-interval ambitus seed

[Function]

Arguments and Values:

size                            an integer (process count).

interval                   an integer (list of intervals).

count                          an integer (number of pitches to process).

pitch                          list of pitches or chords.

max-interval         an integer (maximum interval size).

ambitus         instrument name or an integer or pitch list (low high). The default is 'piano.

seed            NIL or number. The default is NIL.

Description:

This function allows a pitch series to be expanded by interval size and direction. In this preliminary example we'll see the result in pitches and then intervals.

(pitch-expansion-series

4 '(1 -1 2 2) '(1 2) '(c4 g4 g4 db5 ab5))

=>     ((c4 g4 = db5 ab5) (c4 a4 g4 c5 ab5)

; step   original          0  2  0  -1  0

; count                    2

(c4 a4 ab4 c5 g5) (c4 a4 ab4 d5 g5))

; step   0  0   1  0  -1   0  0  0   2  0

; count  2                 1

In this preliminary example we'll see the result in pitches and then intervals. It is important to understand how the direction argument works. with '(1 -1 2 2) - see below.

(pitch-expansion-series

4 '(1 -1 2 2) '(2 3) '(c4 g4 g4 db5 ab5))

=>      (c4 g4 = db5 ab5) (d4 g4 = eb5 ab5

; step   original          2  0  0  2   0

; count                    2

(db4 g4 a4 eb5 ab5) (db4 a4 b4 eb5 bb5))

; step   -1  0  2  0   0     0   2  2  0   2

; count   2                  3

It works particularly well with chords.

(pitch-expansion-series

10 '(1 -1 2 -2) '(1 2 3) 'c4g4g4cs5gs5 :max-interval 6)

=> ((c4 g4 = db5 ab5) (db4 f4 g4 db5 g5) (d4 f4 g4 db5 g5)

(d4 gb4 a4 db5 g5) (d4 e4 bb4 db5 g5) (c4 e4 bb4 db5 g5)

(d4 e4 bb4 db5 g5) (c4 e4 bb4 db5 g5) (c4 gb4 b4 db5 g5)

(c4 gb4 b4 = f5))

(pitch-expansion-series

10 '(1 -1 2 -2) '(1 2 3) 'c4g4g4cs5gs5)

=> ((c4 g4 db5 ab5) (bb3 gb4 db5 ab5) (b3 ab4 c5 ab5)

(c4 ab4 c5 ab5) (c4 ab4 b4 ab5) (c4 ab4 c5 ab5)

(db4 ab4 c5 ab5) (eb4 g4 c5 a5) (eb4 g4 db5 bb5)

(eb4 g4 eb5 b5))

In the example below the 2nd process picks random count 2 (two pitches selected for process) and the two steps (intervals) are 2 and -1.
g4 + 2 semitones = a4
db5 - 1 semitone = c5
```(pitch-expansion-series
4 '(1 -1 2 2) '(2 3) '(c4 g4 g4 db5 ab5))

=>      (c4 g4 = db5 ab5) (d4 g4 = eb5 ab5)
; step   original          2  0  0  2   0
; count                    2
(db4 g4 a4 eb5 ab5) (db4 a4 b4 eb5 bb5)
; step   -1  0  2  0   0     0   2  2  0   2
; count   2                  3```
Each processed list is the master for the next process.
Edited by opmo

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